Field of the Invention
The present invention relates generally to ophthalmic devices and instruments, and specifically to an opaque parabolic hood for reducing the accommodation response of the pupil during eye examinations, including ophthalmic systems containing said parabolic hood and method of using said parabolic hood to reduce accommodation by the pupil and reduce depth of focus in the eye.
Background Information
The accommodation response is elicited when the viewer directs his/her eyes from a distant (e.g., greater than 30 ft away) object to a nearby object. The stimulus is an “out of focus” image. The accommodation (near point) response is consensual (i.e., it involves the action of the muscles of both eyes).
The accommodation response involves three actions:
Pupil accommodation: during accommodation, pupil constriction uses the “pin hole” effect and increases depth of focus of the eye by blocking the light scattered by the periphery of the cornea.
Lens accommodation: lens accommodation increases the curvature of the lens, which increases its refractive (focusing) power.
Convergence in accommodation: when shifting one's view from a distant object to a nearby object, the eyes converge (are directed nasally) to keep the object's image focuses on the foveae of the two eyes.
The normal pupil size in adults varies from 2 to 4 mm in diameter in bright light to 4 to 8 mm in the dark. The pupils are generally equal in size. They constrict to direct illumination (direct response) and to illumination of the opposite eye (consensual response). The pupil dilates in the dark. When a non-occluded eye is looking straight ahead, it will receive visual stimulus of near objects such as equipment, technician, walls, and the like, which would result in pupil constriction of both pupils (consensual response).
All ophthalmic instruments require light to enter the pupil, and image quality is influenced by pupil size. Many instruments on the market are greatly affected by light and pupil size. However, extraneous light (i.e., light that strikes the eye from above or laterally relative to the subject's head) or visual stimulus of near objects causes accommodation stimulus, which again, results in consensual constriction of both pupils. What is needed is an effective method to block these stimuli, as well as reduce depth of focus.